.TH std::ranges::cdata 3 "2024.06.10" "http://cppreference.com" "C++ Standard Libary"
.SH NAME
std::ranges::cdata \- std::ranges::cdata

.SH Synopsis
   Defined in header <ranges>
   Defined in header <iterator>
   inline namespace /*unspecified*/ {

       inline constexpr /*unspecified*/ cdata =            \fI(since C++20)\fP
   /*unspecified*/;                                        (customization point object)

   }
   Call signature
   template< class T >

       requires /* see below */                            \fI(since C++20)\fP

   constexpr /* see below */ cdata( T&& t );

   Returns a pointer to the first element
   of constant type
   (since C++23) of a contiguous range denoted by a
   const-qualified
   (until C++23) argument.

   Let CT be

     * const std::remove_reference_t<T>& if the argument is an lvalue (i.e. T is
       an lvalue reference type),
     * const T otherwise.                                                        (until
                                                                                 C++23)
   A call to ranges::cdata is expression-equivalent to
   ranges::data(static_cast<CT&&>(t)).

   The return type is equivalent to
   std::remove_reference_t<ranges::range_reference_t<CT>>*.

   If the argument is an lvalue or
   ranges::enable_borrowed_range<std::remove_cv_t<T>> is true, then a call to
   ranges::cdata is expression-equivalent to:

     * /*as-const-pointer*/(ranges::data(/*possibly-const-range*/(t))).
                                                                                 (since
   The return type is equivalent to                                              C++23)
   std::remove_reference_t<ranges::range_const_reference_t<T>>*.

   In all other cases, a call to ranges::cdata is ill-formed, which can result
   in substitution failure when the call appears in the immediate context of a
   template instantiation.

   If ranges::cdata(t) is valid, then it returns a pointer to an object
   of constant type
   (since C++23).

  Customization point objects

   The name ranges::cdata denotes a customization point object, which is a const
   function object of a literal semiregular class type. For exposition purposes, the
   cv-unqualified version of its type is denoted as __cdata_fn.

   All instances of __cdata_fn are equal. The effects of invoking different instances
   of type __cdata_fn on the same arguments are equivalent, regardless of whether the
   expression denoting the instance is an lvalue or rvalue, and is const-qualified or
   not (however, a volatile-qualified instance is not required to be invocable). Thus,
   ranges::cdata can be copied freely and its copies can be used interchangeably.

   Given a set of types Args..., if std::declval<Args>()... meet the requirements for
   arguments to ranges::cdata above, __cdata_fn models

     * std::invocable<__cdata_fn, Args...>,
     * std::invocable<const __cdata_fn, Args...>,
     * std::invocable<__cdata_fn&, Args...>, and
     * std::invocable<const __cdata_fn&, Args...>.

   Otherwise, no function call operator of __cdata_fn participates in overload
   resolution.

.SH Example


// Run this code

 #include <cstring>
 #include <iostream>
 #include <ranges>
 #include <string>

 int main()
 {
     std::string src {"hello world!\\n"};

 //  std::ranges::cdata(src)[0] = 'H'; // error, src.data() is treated as read-only
     std::ranges::data(src)[0] = 'H'; // OK, src.data() is a non-const storage

     char dst[20]; // storage for a C-style string
     std::strcpy(dst, std::ranges::cdata(src));
     // [data(src), data(src) + size(src)] is guaranteed to be an NTBS

     std::cout << dst;
 }

.SH Output:

 Hello world!

.SH See also

   ranges::data obtains a pointer to the beginning of a contiguous range
   (C++20)      (customization point object)
   data         obtains the pointer to the underlying array
   \fI(C++17)\fP      \fI(function template)\fP
